He gives the chunk of lapis lazuli to Father David, who puts it on his mantelpiece. ‘You have grown older,’ says the priest, who, alongside his fondness for paradox, has a liking for stating the obvious.

‘Yes,’ says Nicolas. ‘I’ve been thinking it might be time to settle down.’

‘To take a wife?’ says Father David with a mixture of surprise and approval. The priest has an unofficial role as matchmaker in Paris’s small Orthodox community. ‘I know just the family.’

After church on Sundays, Father David hosts small gatherings of his congregants; at one of these he introduces Nicolas to the Rozenfelds. Mr Rozenfeld is a converted Jew from Lvov who owns a chain of fashion boutiques. He’s married to a Polish woman. The two of them have a daughter, Anya, who is training to be a teacher. Petite, dark-eyed and curious, Anya’s nineteen but has the preternatural self-possession of a doted-on only child. She is intrigued by the polite and well-travelled young man. Her parents invite him to stop by for tea and malt loaf.

‘I received an invitation to dine with the head of the Third Section on my return.’

While Nicolas has been away, the previously slipshod operation of the Russian secret police in Paris has been put on a more professional footing. Paris is the destination of choice for the Russian revolutionary in exile. It is, depending on your political outlook, a freethinking Eden of creative dissent or a swamp of ideological contagion that needs to be drained.

The man brought in to head things up is sometimes Pierre, sometimes Pyotr, sometimes Peter; but his last name is always Rachkovsky.

Rachkovsky: it’s worth saying that out loud; a surname to conjure with. Its sound evokes the turn of a key in handcuffs, the click of a lock in a cell door, the scrape of a chair leg on the floor of an interrogation room. Such onomatopoeia, though it fits his job, is strangely discordant with the appearance of the man himself.

He’s five years older than Nicolas, but his age is hard to determine from his face. As genial as a talk-show host, endowed with big appetites for food and sex, he’s large, giggly, bearded, and has black curly hair like lambswool.

At their first encounter, he simply holds Nicolas’s hand and stares at him with unconcealed delight. ‘This is terribly shame-making. I can’t think where to begin. It’s too-too wonderful to meet you. A fellow lottery winner.’

Nicolas has come dressed to the nines and with his hair brilliantined. He is keen to make a good impression and was intending to project gravity and reserve. He’s pitched himself too formally, he realises, and it’s going to take him a few drinks to match Rachkovsky’s energy. ‘A lottery winner?’

Rachkovsky chuckles in a hiccoughing, schoolgirlish way. ‘That’s what I call us! People like us.’ He looks around himself and grins. ‘Here we are! In Paris! For goodness’ sake, somebody pinch me!’ Momentarily distracted by the curve of a waitress’s backside, he follows her motion across the room, and then turns to raise an appreciative eyebrow at Nicolas.